This application claims the benefits of Japanese Application Nos. 10-54576, 10-57102 and 10-127725 which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a rolling bearing unit with a rotation speed detection instrument for use in cars, and to a method for working an outer race for use in the bearing unit.
Particularly, the present invention relates to improvements in a rolling bearing unit with a rotation speed detection instrument which allows a wheel of a car to be supported ratatably on a suspension device thereof and which is used to detect a rotation speed of the wheel, as well as to an outer race constituting the rolling bearing unit with the rotation speed detection instrument.
2. Related Background Art
For rotatably supporting a wheel of a car onto a suspension device, a rolling bearing unit is used. The rotation speed of the wheel must be detected to control an antilock braking system (ABS) as well as a traction control system (TCS). For this reason, it has been widely performed that the foregoing wheel is rotatably supported onto the suspension device by a rolling bearing unit with a rotation speed detection instrument which is built therein and the rotation speed is detected.
Such rolling bearing unit with a rotation speed detection instrument supports a hub on the inner diameter side of its outer race rotatably interposing a plurality of rolling elements between the outer race and the hub.
At the same time, the rotation speed of an encoder fixed to a portion of the hub is detected by a sensor which is supported by a portion of the outer race. The characteristic of the encoder in the circumference direction is changed alternately at equal intervals. Moreover, the technology that the detection portion of the sensor is made to face the outer peripheral surface of a large diameter cylindrical portion of the encoder at a situation where the sensor is supported in a mounting hole formed at an intermediate portion of the outer race in its axial direction and to be elongated in the diameter direction of the outer race, has been widely known as disclosed in, for example, Japanese Patent Laid-open No. 63-59769, 6-109027, 8-270659, and many publications.
When the rolling bearing unit with the rotation speed detection instrument as described above is used, the foregoing outer race is supported on the suspension device, the wheel is fixed to the end portion of the hub, which portion is located a part from the outer race, thereby the wheel being supported rotatably on the foregoing suspension device. When the foregoing encoder rotates with the rotation of the wheel, the output of the sensor having the detection portion facing the encoder changes. The frequency in which the output of the sensor changes is proportional to the rotation speed of the wheel. Therefore, if the output signal of the sensor is sent to a controller which obtains the rotation speed of the wheel, the ABS as well as the TCS can be controlled suitably.
In the case of the rolling bearing unit with the rotation speed detection device described in the foregoing gazettes, no consideration for the compatibility of the workability of the mounting hole with a security of the durability of the outer race was made. Specifically, in order to secure the rolling fatigue life time of the track or raceway of the outer race, a hardened layer having the hardness more than 500 Hv must be formed in the inner peripheral surface of the enter race, and in the surface of the outer race where the outer race tracks are formed and in the vicinity of that surface. This layer is formed to a depth (about 1.5 mm in the case of the rolling bearing unit of cars) more than three times inclusive of three times as large as a depth where a shearing force based on a stress applied by the rolling element becomes maximum (about 0.5 mm in the case of the rolling bearing unit of cars). A transition layer of about 0.5 mm thick exists between the deepest portion of this hardened layer and its so-called raw portion which is not hardened. In this transition layer portion, the hardness gradually decreases from the hardened layer to the raw portion.
In order to form the hardened layer in each of the outer race track portion, although the control of the hardening depth with respect to the thickness direction was considered, the regulation of the formation range of the hardened layer in the surface direction of the inner periphery of the outer race, particularly, in the axial direction, was not considered. Specifically, with respect to the thickness direction, in order to secure the toughness of the outer race, although to leave the raw portion in the vicinity of the outer periphery of the outer race was considered (see, for example, Utility Model Gazette No. 2529597), the consideration in the surface direction was not considered. As described above, when the thickness direction of the hardened layer is considered concerning the range of the hardened layer and the hardened layer is formed in each of the foregoing outer race track portions without considering the surface direction of the hardened layer, the range of the hardened layer may reach to about 10 mm from the end portion of each outer race track or more. The hardness of the hardened layer becomes high in the portion of about 10.5 mm or more apart from the end of each outer race track.
On the other hand, in response to the demand for saving fuel consumption of the cars in recent years, to downsize the rolling bearing unit for supporting the wheel and to reduce a weight of it, the shortening of the dimension of this rolling bearing unit in the axial direction has been developed. Based on such shortening, the distance between the end periphery of each outer race track portion and the mounting hole becomes short, and this distance sometimes can not be kept to be more than 10.5 mm. For this reason, the hardness in the portion where the foregoing mounting hole is to be formed becomes high too, so that working of this mounting hole will be cumbersome. Although the working of this mounting hole may be well performed before the formation of the hardened layer in each outer race track portion, when the hardened treatment is performed after the working of the mounting hole, the considerations for preventing the occurrence of defects due to stress concentration in the mounting hole portion is needed, resulting in troublesomeness of the hardening treatment.
Furthermore, in Utility Model Gazette No. 2529597, the technology is disclosed, in which the hardened layer is formed also in a portion between a plurality of the outer race tracks of the outer race in a part of the inner peripheral surface of the outer race, and the portion between the outer race tracks is made to be not liable to occur a plastic deformation. As described above, when the portion between the outer race tracks is made to be not liable to occur the plastic deformation, the plastic deformation of the outer race is prevented, so that an increase in durability of the rolling bearing unit with the rotation speed detection instrument including this outer race can be achieved, in spite of the fact that an impact load is applied to the outer race due to crashing of the wheel to paving stones. It should be noted that even in such case, toughness of the outer race is secured while leaving a raw portion that is not hardened in the vicinity of the outer periphery of the outer race and occurrence of damages of the outer race such as cracks due to the application of the foregoing impact load can be prevented.
However, when the hardened layer is formed also between the outer race tracks in the part of the inner peripheral surface of the outer race, working of the mounting hole to fixedly support the sensor, which is formed in the outer race, becomes difficult.
On the other hand, in response to the demand for saving fuel consumption of the cars in recent years, to downsize the rolling bearing unit for supporting the wheel and to reduce a weight of it, the shortening of the dimension of this rolling bearing unit in the axial direction has been developed. Based on such shortening, the distance between the end periphery of each outer race track portion and the mounting hole becomes short, and this distance sometimes can not be kept to be more than 10.5 mm. For this reason, the hardness in the portion where the foregoing mounting hole is to be formed becomes high too, so that working of this mounting hole will be cumbersome. Although working of this mounting hole may be well performed before the formation of the hardened layer in each outer race track portion, when the hardening treatment is performed after the working of the mounting hole, the considerations for preventing the occurrence of defects due to stress concentration in the mounting hole portion is needed, resulting in troublesomeness of the hardening treatment.
Furthermore, as described in the foregoing Utility Model Gazette No. 2529597, the technology has been known, in which the hardened layer is formed also between a plurality of the tracks of the outer race in order to enhance the durability of the rolling bearing unit with the rotation speed detection instrument including the outer race by making the outer race not liable to occur the plastic deformation, even when an impact load is applied to the outer race through the hub and the rolling element owing to reasons such as crashing of the wheel against the paving stone. As described above, in the case where the hardened layer is formed also between a plurality of the outer race tracks of the outer race, the working of the foregoing mounting hole becomes cumbersome, not only in the case of small-sized rolling bearing units but also even in the case of comparatively large-sized rolling bearing unit with the rotation speed detection instrument in which the distance between the end periphery of each outer race track portion formed in the inner periphery surface of the outer race and the mounting hole, is relatively large.
From the viewpoint of the above described circumstances, the first object of the present invention is to provide a rolling bearing unit with a rotation speed detection instrument which is capable of performing the working operation particularly for the foregoing mounting hole without making the hardening treatment troublesome.
The rolling bearing unit with a rotation speed detection instrument to achieve the first object comprises a hub rotating together with a wheel at the time of its use, the hub having a plurality of inner race tracks in an outer peripheral surface thereof; an outer race formed of steel material, which at the time of its use, is supported stationary by a suspension device and does not rotates the outer race having a plurality of outer race tracks in an inner peripheral surface to face the inner race tracks; rolling elements, each being rotatably provided between the inner race track and the corresponding outer race track; an encoder fixedly fitted on a portion of the outer peripheral surface of the hub arid between the inner race tracks, the encoder exhibiting a characteristic which changes in its circumference direction alternately at equal intervals; and a sensor having a detecting section, the sensor being supported in a mounting hole provided in an intermediate portion of the outer race in its axial direction to face the encoder and changing its output signal in response to the change of the characteristic of the encoder, wherein a hardened layer is formed in each outer race track portion in the inner peripheral surface of the outer race.
Particularly, the present invention is directed to the rolling bearing unit with the rotation speed detection instrument in which the distance between the mounting hole and an end periphery of the outer race track closest to the mounting hole among the plural outer race tracks is 10.5 mm or less. In this rolling bearing unit with the rotation speed detection instrument, the portion where the mounting hole is formed is not hardened, and a hardened layer formed in the outer race track closest to the mounting hole has a thickness of 1.5 mm or more.
Furthermore, it is perferable that, in the rolling bearing unit with the rotation speed detection instrument, the distance between the mounting hole and the end periphery of the outer race track closest to the mounting hole among the outer race tracks is at a range from 2 to 10.5 mm, and the minimum distance between the mounting hole and the hardened layer, which is formed in each outer race track portion and has a hardness of 500 Hv or more, is 0.5 mm or more.
In this case, a working operation for the mounting hole to mount or support the sensor in the outer race can be easily performed without degrading the durability of each outer race track portion as well as without making a hardening treatment for each outer race track portion troublesome. Specifically, since the mounting hole portion is not subjected to hardening, the working of the mounting hole can be easily performed.
When the distance between the mounting hole and the end periphery of the outer race track close to this mounting hole is set to 2 mm or more, the minimum thickness of 1.5 mm for the hardened layer formed in each outer race track portion, which is necessary for securing the durability of each outer race track, can be secured. Furthermore, by setting the minimum distance between the mounting hole and the hardened layer formed in each outer race track portion to 0.5 mm or more, the mounting hole can be formed in a raw material portion apart from a transition layer or at least in a semi-raw portion exhibiting a low hardness, and even after the hardened layer is formed in each outer race track portion, the working of the mounting hole can be easily performed.
It is perferable that in the rolling bearing unit with the rotation speed detection instrument to achieve the first object, the hardened layers provided in the portions where the outer race tracks are formed are connected by a jointing hardened layer provided at a position apart from the mounting hole in its circumference direction, which has a hardness of 500 Hv or more, and the minimum distance between the jointing hardened layer and the mounting hole is 0.5 mm or more.
According to the rolling bearing unit with the rotation speed detection instrument last described, even when an impact load is applied to the outer race through the hub and the rolling elements, the outer race does not tend to make a plastic deformation, and the working of the mounting hole can be in addition easily performed.
By virtue of the rotation bearing unit with the rotation speed detection instrument to achieve the first object, which is constructed as described above, a wheel is supported rotatably on the suspension device, and an operation to detect the rotation speed of the wheel is conducted similarly to that of the case of the conventional rotation bearing unit with a rotation speed detection instrument, which has been well known.
By the way, in the case of the rolling bearing unit with the rotation speed detection instrument in which the hardened layer is formed also in the position between the plural outer race tracks in the inner periphery surface of the outer race, the working of the mounting hole formed in the outer race to fixedly support the sensor becomes difficult.
Accordingly, the second object of the present invention is to provide a working method of an outer race for use in a rolling bearing unit with a rotation speed detection instrument which makes it possible to work a sensor mounting hole even when a hardened layer is formed not only in the portions where the outer race tracks are formed but also between a plurality of the outer race track portions in an inner peripheal surface of an outer race, an outer race obtained by this method, and a rolling bearing unit with a rotation speed detection instrument obtained by this method.
Furthermore, aiming at securing toughness of the outer race and preventing occurrence of damages such as cracks in the outer race regardless of an impact load which may be applied during running of cars, in order to leave a raw portion which is not hardened by hardening in the vicinity of an outer diameter side of the portion between the outer race tracks in a part of the outer race, a hardened layer must be formed in an inner peripheral surface of the outer race while cooling an outer peripheral surface of the outer race with coolant. A further object of the present invention is to provide a working method which is capable of preventing the occurrence of unevenness of the hardened layer due to an invasion of the coolant into the inner peripheral surface of the outer race.
A rolling bearing unit with a rotation speed detection instrument to achieve the second object of the present invention comprises; a hub rotating together with a wheel at the time of its use, the hub having a plurality of inner race tracks in an outer peripheral surface thereof; an outer race which, at the time of its use, is supported stationary by a suspension device and does not rotates, the outer race having a plurality of outer race tracks in an inner peripheral surface of the outer race to face the inner race tracks; rolling elements, each being rotatably provided between the inner race track and the corresponding outer race track; an encoder fixedly fitted on a portion of the outer peripheral surface of the hub between the inner race tracks, the encoder exhibiting a characteristic which changes in its circumference direction alternately at equal intervals; and a sensor having a detecting section, the sensor being supported in a mounting hole provided in an intermediate portion of the outer race in its axial direction in a state where the detecting section faces the encoder and changing its output signal in response to the change of the characteristic of the encoder, and wherein a hardened layer is formed in the portions where the outer race tracks are formed and in the portion between the outer race tracks, in the inner peripheral surface of the outer race, and the mounting hole is formed using a drill having a super-hard drill or a ceramic chip, while cooling and lubricating a cut portion by cutting oil.
Furthermore, in a method for working the outer race constituting the foregoing rolling bearing unit with the rotation speed detection instrument is preferably performed in such manner that the hardened layer in the portions of the outer race where the plural outer race tracks are formed in the inner peripheral surface of the outer race and a portion between both the outer race tracks is formed, and thereafter a mounting hole is formed in the intermediate of the outer race in the axial direction thereof and between the plural outer race track portions, using an ultrahard drill or a drill provided with a ceramic clip, while cooling and lubricating a cut portion by cutting oil.
In a method of working the outer race of the rolling bearing unit with the rotation speed detection instrument, it is preferable that the hardened layer in the inner peripheral surface of the outer race and at the portions where the outer race tracks are formed and at the portion between both the outer race tracks, is formed while cooling said outer race from the outer periperal surface side by coolant, and a cutting speed of the drill for forming a mounting hole is 20 m/min. or less expressed by speed of an outer peripheral surface of the drill.
In the rolling bearing unit with the rotation speed detection instrument to achieve the second object, in a situation where the mounting hole is formed from the outer peripheral surface side of the outer race to a certain portion in a diameter direction of the outer race, the hardened layer can be formed by heating the inner peripheral surface of the outer race while cooling the outer race from its outer peripheral surface side by coolant, and the mounting hole can be completed by perforating through to the inner peripheral surface of the outer race after the hardened layer is formed.
In a method for working an outer race constituting the rolling bearing unit with the rotation speed detection instrument to achieve the second object, it is preferable that after the mounting hole is formed from the outer peripheral surface side of the outer race to a certain portion in a diameter direction of the outer race, the hardened layer is formed by heating the inner peripheral surface of the outer race while cooling the outer race from its outer peripheral surface side by coolant, and the mounting hole is completed by perforating through to the inner peripheral surface of the outer race after the hardened layer is formed.
In the rolling bearing unit with the rotation speed detection instrument to achieve the second object, after the mounting hole is formed, the hardened layer may be formed by heating the inner peripheral surface of the outer race while cooling the outer peripheral surface of the outer race by coolant in a state where the mounting hole is hermetically sealed or substantially sealed by a plug.
In a method for working the outer race constituting the rolling bearing unit with the rotation speed detection instrument to achieve the second object, after the mounting hole is formed at a portion between the outer race tracks, in an intermediate portion of the outer race in its axial direction, the hardened layer may be formed by heating the inner peripheral surface of the outer race while cooling the outer peripheral surface of the outer race by coolant in a state where the mounting hole is hermetically sealed or substantially sealed by a plug.
In the rolling bearing unit with a rotation speed detection instrument to achieve the second object, after the mounting hole is formed, the hardened layer may be formed by, while rotating the outer race, heating the inner peripheral surface of the outer race and cooling the outer peripheral surface of the outer race by coolant blown upward.
In a method for working the outer race constituting the rolling bearing unit with the rotation speed detection instrument to achieve the second object, after the mounting hole is formed in an intermediate portion of the outer race in its axial direction and at a portion between the outer race tracks, the hardened layer may be formed by, while rotating the outer race, heating the inner peripheral surface of the outer race and cooling the outer peripheral surface of the outer race by coolant blown upward.
In the rolling bearing unit with the rotation speed detection instrument to achieve the second object, after the mounting hole is formed, the hardened layer may be formed by heating the inner peripheral surface of the outer race while cooling the outer peripheral surface of the outer race by gaseous coolant.
In a method for working the outer race constituting the rolling bearing unit with the rotation speed detection instrument, after the mounting hole is formed in an intermediate portion of the outer race in its axial direction and at a portion between the outer race tracks, the hardened layer may be formed by heating the inner peripheral surface of the outer race while cooling the outer peripheral surface of the outer race by gaseous coolant.
According to the bearing unit with the rotation speed detection instrument and the method for working the outer race for use in the bearing unit with the rotation speed detection instrument to achieve the second object, the mounting hole for fixedly supporting the sensor may be formed even in the outer race provided with the hardened layer for preventing deformation. Therefore, a bearing unit with a rotation speed detection instrument which comprises an outer race which is not apt to deform due to a impact and fixedly supports a sensor in the mounting hole formed in the intermediate portion of the outer race in its axial direction can be realized.
By the bearing unit with the rotation speed detection instrument to achieve the second object, which comprises the outer race formed as described above, a wheel is rotatably supported on the suspension device, and an operation when the rotation speed of the wheel is detected is the same as that of the well known conventional bearing unit with the rotation speed detection instrument.